In the drilling and completion industry, the formation of boreholes for the purpose of production or injection of fluid is common. The boreholes are used for exploration or extraction of natural resources such as hydrocarbons, oil, gas, water, and alternatively for CO2 sequestration.
To increase the production from a borehole, the production zone can be fractured to allow the formation fluids to flow more freely from the formation to the borehole. The fracturing operation includes pumping fracturing fluids including proppants at high pressure towards the formation to form and retain formation fractures. A conventional fracturing system passes pressurized fracturing fluid through a tubular string that extends downhole through the borehole that traverses the zones to be fractured. The string may include valves that are opened to allow for the fracturing fluid to be directed towards a targeted zone. To remotely open the valve from the surface, a ball is dropped into the string and lands on a ball seat associated with a particular valve to block fluid flow through the string downhole of the ball and consequently build up pressure uphole of the ball which forces a sleeve to move in a downhole direction thus opening a frac port in the wall of the string. When multiple zones are involved, the ball seats are of varying sizes with a downhole-most seat being the smallest and an uphole-most seat being the largest, such that balls of increasing diameter are sequentially dropped into the string to sequentially open the valves from the downhole end to an uphole end. Thus, the zones of the borehole are fractured in a “bottom-up” approach by starting with fracturing a downhole-most zone and working upwards towards an uphole-most zone.
Because hydrocarbon production wells are often drilled into unconsolidated formations, sand and fines from those formations will tend to enter the production tubing along with the produced fluids. To prevent this, a fracturing and gravel packing treatment can be performed, commonly referred to as a “frac pack,” within the wellbore prior to production.
A conventional frac pack system includes a screen assembly that is placed in the wellbore near the unconsolidated formation. The screen assembly radially surrounds a wash pipe, and both the screen assembly and wash pipe are connected, at their upper ends, to a service tool. The usual service tool includes a production packer and a cross-over tool, which are connected to a work string that extends downwardly from the surface. The work string is used to position the screen assembly in the wellbore. Packers provide fluid sealing. The frac pack system can be placed into a “squeeze” configuration, wherein no fluids return to the surface. In this configuration, fracturing fluid is passed through the cross-over tool, into the annulus and then into the formation. Alternately, the frac pack system can be placed into a “circulation” position to allow flow through the wash pipe back to the surface. Gravel packing slurry is then flowed in through the cross-over tool to gravel pack the annulus around the screen assembly. The gravel collects around the screen to form the gravel pack. The gravel allows flow of produced fluids there through and into the screen while blocking the flow of particulates produced with the formation fluids. When gravel packing is completed, the service tool is detached from the screen assembly and withdrawn from the wellbore, leaving the gravel packed screen assembly and packer in place.
The art would be receptive to improvements in frac and gravel packing systems and methods.